Title

Author

Defense Date

2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Vamsi Yadavalli

Abstract

Silk proteins have provided a source of unique and versatile building blocks in the fabrication of biomedical devices for addressing a range of applications. Critical to advancing this field is the ability to establish an understanding of these proteins in their native and engineered states as well as in developing scalable processing strategies, which can fully exploit or enhance the stability, structure, and functionality of the two constituent proteins, silk fibroin and sericin. The research outlined in this dissertation focuses on the evolution in architecture and capability of silks, to effectively position a functionally-diverse, renewable class of silk materials within the rapidly expanding field of smart biomaterials. Study of the process of building macroscopic silk fibers provides insight into the initial steps in the broader picture of silk assembly, yielding biomaterials with greatly improved attributes in the assembled state over those of protein precursors alone. Self-organization processes in silk proteins enable their aggregation into highly organized architectures through simple, physical association processes. In this work, a model is developed for the process of aqueous behavior and aggregation, and subsequent two-dimensional behavior of natural silk sericin, to enable formation of a range of distinct, complex architectures. This model is then translated to an engineered system of fibroin microparticles, demonstrating the role of similar phenomena in creating autonomously-organized structures, providing key insight into future “bottom up” assembly strategies. The aqueous behavior of the water-soluble silk sericin protein was then exploited to create biocomposites capable of enhanced response and biocompatibility, through a novel protein-template strategy. In this work, sericin was added to the biocompatible and biodegradable poly(amino acid), poly(aspartic acid), to improve its pH-dependent swelling response. This work demonstrated the production of a range of porous scaffolds capable providing meaningful response to environmental stimuli, with application in tissue engineering scaffolds and biosensing technologies. Finally, to expand the capabilities of silk proteins beyond process-driven parameters to directly fabricate engineered architectures, a method for silk photopatterning was explored, enabling the direct fabrication of biologically-relevant structures at the micro and nanoscales. Using a facile bioconjugation strategy, native silk proteins could be transformed into proteins with a photoactive capacity. The well-established platform of photolithography could then be incorporated into fabrication strategies to produce a range of architectures capable of addressing spatially-directed material requirements in cell culture and further applications in the use of non-toxic, renewable biological materials.